A mobile terminal has a small volume, so its internal circuit design and Printed Circuit Board PCB layout are greatly limited. A COder-DECoder codec and a stereo sound output port of many mobile terminals are at a far distance and even on different PCBs, which causes a large impedance between the codec and the stereo sound output port. Especially, the impedances from the stereo sound output port and its matched return current ground to the codec are comparatively large. If a small-impedance sound production device is connected with the stereo sound output port, for example, a 16-ohm or a 32-ohm headphone, and since a left channel and a right channel share the common return current ground, a divided voltage of an electrical signal of the left channel on the return current ground will affect the right channel, and vice versa. When listening to stereo music, the fidelity of music signals of the left and right channels will be distorted. The difference of frequencies, phases and amplitudes of the sound signals of the left and right channels causes a severe crosstalk, so the sound quality of stereo sound is deteriorated, and even the user listening experience is seriously affected.
The existing method for improving the stereo sound crosstalk of a terminal is to reduce the impedance from the return current ground of the stereo sound output port to the codec as possible, and widen lines, or try to make sure that the stereo sound output port and its return current ground and the codec are on the same PCB. The method will bring a very significant influence on the PCB layout of the terminal and even the degree of freedom of Industrial Design ID, for example, a headphone jack is constrainedly designed near the codec on the PCB, but according to that, form the appearance, the position of the headphone jack on the terminal is not reasonable. Or the number of PCBs is increased to reduce a return current impedance Rgnd, but the cost of the terminal is increased.
Or, an extra codec chip is adopted and designed near the stereo sound port of the terminal, but this method still increases the cost and the pressure of the PCB layout.
The existing art has the following problem: whether the measure of reducing the impedance from the return current ground of the stereo sound output port to the codec or the measure of adopting the extra codec chip will increase the cost and affect the PCB layout.